1. Field of the Invention
This invention relates to an improved continuous, low pressure ethynylation process for the production of butynediol.
2. Description of the Prior Art
Butynediol has been prepared in the past by an ethynylation reaction in which formaldehyde and acetylene are reacted in the presence of an ethynylation catalyst. Such processes are described, for example, in U.S. Pat. Nos. 2,232,867, 2,300,969, 2,487,069, 2,712,560, 2,768,215, 3,108,140, 3,294,849, 3,560,576, 3,920,759 and Ger. DAS No. 2,206,693.
The ethynylation reaction generally employs some form of complex cuprous acetylide catalyst, either supported or unsupported, which catalyst may be generated or made active by a variety of methods and from a variety of copper compounds. Often the complex cuprous acetylide catalysts are used together with a bismuth compound to minimize undesired cuprene formation, cuprene being a product resulting from undesired actylene polymerization. The precursor material of the supported catalysts customarily used in the manufacture of butynediol are produced by impregnating the support with solutions of cupric and bismuth salts, such as the nitrates, drying, and calcining to produce the corresponding metal oxides. The cupric oxide thereafter is converted to the active complex cuprous acetylide catalyst in situ by suitable treatment with acetylene and formaldehyde.
In U.S. Pat. No. 3,920,759, a low pressure ethynylation process is described which utilizes as a catalyst an aqueous slurry of finely-divided complex cuprous acetylide supported on a magnesium silicate carrier, under intense agitation, to provide butynediol at a high rate of production under safe conditions. Nevertheless, it would be advantageous to provide an improved, and particularly a more continuous low pressure process, of the type described in U.S. Pat. No. 3,920,759, specifically with respect to the means by which the butynediol product may be separated from the catalyst slurry as a catalyst-free clear liquid stream, and by which the separated concentrated catalyst slurry may be effectively continuously and immediately recycled to the reaction zone, thereby to make the process more continuous than has been possible heretofore.
Since the average or mean particle size of the precursor material of the finely-divided magnesium silicate-supported complex cuprous acetylide catalyst ranges from about 1 to about 1,000 microns, usually from about 1 to about 200 microns, and the ethynylation reaction product mixture contains a high catalyst solids content, usually about 3 to about 30 weight % of the mixture, separation is difficult. Thus, while some filtering devices, such as a centrifuge, might be utilized to produce a high solids-catalyst recycle stream, centrifugation would not be able to produce a catalyst-free liquid product stream of sufficient clarity to be used directly in other operations. Moreover, while other continuous filter devices, such as a rotary drum filter, might produce the required clarity, such a filtration device would also produce a semi-solid catalyst that would have to be reslurried externally in a separate step, prior to recycle, a significant economic penalty.
For a separation means to satisfy the requirements of adequately removing the catalyst solids suspended in the reaction product mixture which is withdrawn from the reaction zone, for purposes of the present invention, such means has to meet at least the following rigid criteria: (1) it has to be capable of separating catalyst particles as small as those having a diameter of one micron; (2) it has to be capable of processing, safely, a catalyst-containing reaction product mixture that is saturated with acetylene; (3) it has to be capable of separating the mixture continuously into a catalyst-free or clear filtrate fraction, and a catalyst-containing fraction in the form of a flowable concentrated catalyst slurry that can be continuously and immediately recycled to the ethynylation reaction zone; (4) it must not deactivate the ethynylation catalyst during the separation process, for example, it must not induce acetylene starvation, which would cause the cuprous acetylide content of the catalyst to be reduced to elemental copper and be extracted in the filtrate, a potentially dangerous and explosive situation; and (5) it has to be capable of providing sufficient separation rates so as to provide favorable overall process economics.